"Since the law is new, it is too early to say there is an increasing trend," he said.

Last year, the rules governing cross-border vehicles were loosened, to allow more ordinary people to travel to the mainland in their own cars.

Under the scheme, Hong Kong residents can drive a car with five seats into Guangdong Province via the Shenzhen Bay Port once, for a stay of not more than seven days.

There are now fears such vehicles might be used to smuggle infant milk formula.

Under the new rules to protect local babies' supply of infant milk formula, passengers over the age of 16 can take only two tins, or 1.8kg, of infant milk formula out of Hong Kong on their first trip out of the city in 24 hours.

On Saturday, a 47-year-old mainland man was the first to be penalised under the new rule, after he was found with 11 cans of formula at the Shenzhen Bay control point. He was fined HK$5,000.

Yesterday, one person was caught with two sachets of milk powder totalling 2.4kg.

Travellers were earlier seen outside Sheung Shui train station repackaging cartons of baby formula in an apparent attempt to evade the government's new limits.

Three people have pleaded guilty to contravening the Import and Export (General)(Amendment) Regulation 2013 and are awaiting sentencing, Lai said.

Police are also looking for two non-Chinese men who early yesterday morning stole nine cans of milk powder, worth HK$2,400, from premises in Nathan Road, Tsim Sha Tsui.